I have an sendmail server, sitting in front of my Exchange server. This server filters spam with SpamAssassin (and does it incredibly well!), but it merely tags spam messages with appropriate header flags and by modifying the message subject. When such a message arrives a to user mailbox on the Exchange server, where it is examined by Exchange/Outlook junk e-mail filter, which puts most of the spam in the junk message folder.
And that is my problem: most, but not all! To put all spam in the junk mail folder the user has to define an rule, saying e.g:
"If header contains text 'X-Spam-Flag: YES' then move it to 'Junk e-mail messages' folder".
Fine, but it has to be done on every user (for some users, this task is too "complicated" to do for themselves. :-)
So, I want to know, how could I modify the message header in such a way, that the Exchange junk e-mail filter will recognize this message 100% for certain as spam, freeing the user from the task of defining his own rule.
A solution could result from defining such a rule by using AD and group policy, but I wan't to avoid this due to many possible caveats. There are so many combinations of different operating systems and different Outlook versions, and to be honest, I doubt if it is even possible.